Add Unix tools to path; Add C++ build tools; Drop msys2

[k0ekk0ek]

This PR:

1. Adds the Unix tools to the path on installation to enable use of CIRRUS_SHEL: bash so that the same shell environment can be used across platforms;
2. Adds visualstudio2019-workload-vctools to allow users to compile with MSVC;
3. Drops msys2 to avoid indefinite hangs of Docker.

• Trick to reenable visualstudio2019-workload-vctools is to depend on an older version of dotnetfx. The latest version has known problems and causes the Visual Studio installer to fail.
• Reasoning behind dropping msys2 is that it isn't required since the Unix tools that ship with Git are available already and mingw is installed separately.

This should solve #12, #13 and #14. Additionally diff becomes available and thus should make #11 obsolete. I did a test build before, but this one should report success imminently.

[fkorotkov]

Wow! Thank you, @k0ekk0ek! I tried to fix the build but was not able. Will rebuild VMs that Cirrus is using to have the new images pre-cached on them to speed up startup time.

[k0ekk0ek]

Thanks @fkorotkov!

[k0ekk0ek]

@fkorotkov, could it be that GCE still has the older image cached? visualstudio2019-workload-vctools is notably absent. Not to rush you of course, but could it be that a "flush cache" button needs to be pressed somewhere?

choco list --local-only
Chocolatey v0.10.15
7zip 19.0
7zip.install 19.0
chocolatey 0.10.15
chocolatey-core.extension 1.3.5.1
chocolatey-dotnetfx.extension 1.0.1
chocolatey-visualstudio.extension 1.8.1
chocolatey-windowsupdate.extension 1.0.4
cmake.install 3.19.1
dotnetfx 4.8.0.20190930
git 2.28.0
git.install 2.28.0
KB2919355 1.0.20160915
KB2919442 1.0.20160915
KB2999226 1.0.20181019
KB3033929 1.0.5
KB3035131 1.0.3
python3 3.9.0
vcredist140 14.28.29325.2
vcredist2015 14.0.24215.20170201
visualstudio-installer 2.0.1
visualstudio2019buildtools 16.7.0.0
visualstudio2019community 16.7.0.0
winflexbison3 2.5.23.20200904
23 packages installed.

[fkorotkov]

Just rebuilt the base images that runs Windows containers, should be working now! Sorry for the delay.

[ericoporto]

I think this PR may have broken my workflow on #16 .

[ped7g]

This seem generally help with all my windows-build issues, except I can't find the MSCC in the image?
(I can find gcc8.1 in mingw64, and bash/diff/cmp/find/... GNU utilities in Git folder)

https://cirrus-ci.com/task/5883284922040320?command=build#L188

Seems there is Roslyn (C#? compiler?) and msbuild.exe, but no cl.exe or vcvars*.bat

From reading the package visualstudio2019-workload-vctools description it looks to me like that's the main purpose of it, so something went wrong somewhere? Or I'm just blind?